Physico-chemical and microbial processes governing the decay of organic substance in sediment under anoxic conditions

为了使海洋类群的软组织成为化石，身体必须迅速转移到缺氧的条件下，并与潜在的食腐动物隔离开来。要做到这一点，一种可行的方法是将腐烂的身体或活的固着物种埋葬在沉积物中。沉积物中的有机碳被氧化成HCO3-和CO32-，将减少沉积物和海水中的主要电子受体，即铁和硫酸盐。衰变反应将在身体周围产生局部Eh和pH光晕，其中可能稳定FeS硫化物、菱铁矿和其他碳酸盐相。然后，这些相可以取代或模板化有机组织，或者将有机物质包裹在固结中。在2685年度的研究单位内，申请者将制定实验程序，允许就地调查海洋沉积物中鱼类和棘皮动物的缺氧腐烂情况。其主要目标是量化可进行更替的比率。在实验进行期间，会不时对有机物质进行采样。无机沉淀物将通过拉曼光谱进行鉴定。新出现的细菌群落将以与研究单位成员的密切合作为特征。预计无机材料-FeS相、菱铁矿、方解石-的模板化可能需要几周到几个月的时间。细菌群落的特征是本提案的一个重要方面，它将阐明伪形置换反应是性质上的无机反应，只受pH和Eh梯度的驱动，还是必须由细菌介导才能有效。

To fossilize soft tissue of marine taxa it is essential that a carcass be transferred rapidly to anoxic conditions and isolated from potential scavengers. A practical way to achieve this is by burying a decaying carcass or a living sessile species in sediment. The oxidation of organic carbon to HCO3- and CO32- within the sediment will reduce the major electron acceptors in sediment and seawater, i.e. ferric iron and sulfate. The decay reactions will create local Eh and pH haloes around a carcass within which FeS sulfide, siderite, and other carbonate phases may be stabilized. These phases may then replace or template organic tissue, or encase the organic material in concretions. Within the research unit FOR 2685 the applicant will develop experimental routines that allow to investigate in-situ the anoxic decay of fish and echinoderms within a marine sediment. The major aim is to quantify the rates by which replacement can take place. While an experiment is progressing, organic material will be sampled from time to time. Inorganic precipitates will be identified by Raman spectroscopy. Bacterial communities emerging will be characterised in close collaboration with members of the research unit. It is expected that the templation by inorganic material - FeS phases, siderite, calcite - may be a matter of weeks to months. The characterisation of bacterial communities, an important aspect in the present proposal, will elucidate if pseudomorphic replacement reaction are inorganic by nature and driven only by pH and Eh gradients, or if they must be mediated by bacteria in order to be efficient.